FIG. 1 shows a circulating water heating system 1.000, which is contained within an appliance 1.100 schematically represented by a dash and two dot surrounding line. The system has one or more water heaters 1.001a . . . 1.001n, each having a heater inlet 1.022 and a heater outlet 1.023. The water heaters can be instantaneous water heaters, which heat the water only when water is drawn off by the users of the system. Each heater inlet 1.022 is connected to a system inlet pipe 1.002. The system inlet pipe 1.002 is connected to mains water supply or preheated water source 1.0022 via an appliance inlet fitting at 1.0021, and via which water to be heated is fed into the system. Each heater outlet 1.023 is connected to a hot water delivery pipe 1.003 which is connected to a hot water outlet fitting 1.0031 on the outside of the appliance 1.100. The hot water delivery pipe 1.003 is thus connected via fitting 1.0031 and a building hot water distribution network 1.024, to a number of user outlets or heat exchanger devices 1.004 via, to permit users to draw off hot water. Each water heater can have an adjustable and or controllable water control valve to control flow of water through the water heater. Each water heater can have a flow sensor which can operate the associated water heater when flow is detected.
The water heaters 1.001a . . . 1.001n can have a controllable gas valve and ignition means. The ignition means can be any suitable ignition means such as a pilot flame. The ignition means can be a controllable ignition means such as a spark generator.
The water heaters are connected in parallel between the system inlet pipe 1.002 and the hot water delivery pipe 1.003.
A closed loop hot water supply-return circuit forms a closed circuit with the hot water delivery pipe 1.003, the building hot water distribution network 1.024, which connects back to the appliance 1.100 via a hot water return inlet fitting at 1.0061, which in turn connects to a hot water return pipe 1.006 then system inlet pipe 1.002 and water heaters 1.001a . . . 1.001n. A pump 1.005 is adapted to circulate water through the water heaters 1.001a . . . 1.001n, the hot water delivery pipe 1.003, building hot water distribution network 1.024 and the hot water return pipe 1.006. The hot water return pipe 1.006 connects to the system inlet pipe 1.002 so the pump can increase the pressure at the heater inlets 1.022.
A non-return valve 1.007 inhibits reverse flow through the hot water return pipe 1.006, so cold water from main water supply cannot bypass the water heaters and reach the user outlets 1.004 via the hot water return pipe 1.006 and the building hot water distribution network 1.024.
The pump can be used to circulate water through the water heaters 1.001a . . . 1.001n to maintain the temperature of the water in the close loop hot water supply-return circuit above a first threshold temperature, so that, when user outlets or heat exchanger devices 1.004 are activated, such as by opening a hot water tap, the water will be at a required temperature.
A single water heater can adequately heat a first level of consumption, while two water heaters are required to meet a demand which exceeds the capacity of a single water heater, and so on. The capacity of each water heater is a known design factor.
Each water heater can have its own flow sensor although a single flow sensor can be used in the hot water delivery pipe 1.003 or in the system inlet pipe 1.002.
Each water heater can have a maximum input capacity or flow rating. The water heater is designed to heat water at a flow rate up to the maximum flow rate to a specified temperature rise. If the flow through the water heater exceeds this input capacity, the water heater cannot heat the water to the required temperature. The water heater can also be designed to have a greater the pressure drop across the water heater when the flow exceeds the maximum flow rate. As the water heaters are in parallel, then, assuming “n” water heaters of the same design, the maximum flow rate for the combination of water heaters to heat water to the required temperature will be n times the flow rate of a single water heater.
The pump can be run continuously, or run according to a timer setting, and one of the water heaters or all water heaters are maintained operational, so that the pump can circulate hot water through the hot water delivery pipe 1.003, the building hot water distribution network 1.024 and hot water return pipe 1.006, to ensure that hot water is immediately available at the user outlets 1.004, such as shower taps.
In order to avoid the delivery of water at a temperature below the specified temperature, flow control means can be used to limit the flow of water through the water heaters to a predetermined maximum flow. While this may avoid the problem of delivering water at a lower than specified temperature, it results in a drop in the pressure of the hot water delivered to the user outlets or heat exchanger devices 1.004.
The present invention proposes an arrangement to mitigate the effects of decreased hot water pressure at high flow rates.